Known in the art are player pianos or the like apparatuses. A player piano is an acoustic piano wherein the keys are actuated by a built-in or an externally attached actuator unit including solenoid plungers or the like in accordance with the recorded music playing data such as punched holes on a piano roll and MIDI data on a storage medium, the keys in turn actuating the corresponding piano action hammers to strike the corresponding piano strings, thereby conducting an automatic performance of piano music. An example of such an actuator unit is disclosed in the specification of U.S. Pat. No. 5,861,566 (corresponding to unexamined Japanese patent publication No. H9-237082).
Also known in the art are electronic musical instruments having electronic tone generators wherein the tone generators generate musical tones in accordance with music playing data to conduct an automatic music performance. The music playing data may preferably be of a MIDI format, and may be externally inputted (e.g. from a sequencer) or may be transferred from an external music work source via a communication network or via a storage medium to a music playing data processing circuit (sometimes further via an internal memory) so that the read-out music playing data control the tone generators to conduct an automatic music performance.
In the case of an electronic musical instrument, an automatic music performance can be conducted without actuating the keys in the keyboard, contrary to the case of an acoustic piano. Recently, however, there is a desire that the keys should move along with the tone generation by the tone generator circuits to visually enjoy the progressing automatic music performance in addition to aural enjoyment of the music. Electronic musical instruments having keys which move along with the progressing automatic music performance conducted by music performance data signals are disclosed, for example, in unexamined Japanese patent publication No. 2004-29549 and in unexamined Japanese patent publication No. 2005-55541.
In the first one of the above referenced publications, the solenoids for actuating the keys are provided near the rear end of the keys at the area away (as viewed from the player) from the swing fulcrum. In the acoustic piano, the swing fulcrum for the keys resides on the middle rail carrying balance pins, and accordingly a space for placing the solenoid units can be easily prepared in the area away from the middle rail.
In the electronic piano disclosed in the second one of the above referenced publications, a key arm is extended from the key rearward than the swing fulcrum (pivot) of the key, and the rear end of the extended key arm is actuated by the solenoid plunger. This necessitates the space beyond the key and the size of the instrument body will be increased accordingly, and the general merit of an electronic piano as being compact will be impaired.
In the electronic piano disclosed in the third one of the above referenced publications, a swing weight mechanism is provided underneath the key and a solenoid plunger actuates the swing weight mechanism from below. This structure solves the problem of the size increase. However, as the keyboard assembly of the electronic piano is placed on the key bed, the provision of such an actuator below the keyboard assembly will cause a substantial protrusion from the key bed.
Thickening the key bed or the similar case structure would avoid such protrusion of actuators, there will be a limit in thickening the instrument body around the keyboard, as the player of the instrument needs to push in the knees and the legs to manipulate the pedals in the case of an electronic piano. It is therefore required to minimize the vertical sizes of the actuators and to devise the body structure of the instrument below the keyboard. The third one of the above referenced publication does not teach the details of the actuators and the body structure of the instrument below the keyboard.